Computer Cart

ABSTRACT

A computer cart has removable electrical connector management system which may be removed from the computer cart to install portable electronic device electrical transformers, and then reinserted into the computer cart to enable multiple electrical transformers to be installed into the cart as a group. An electrical charging system uses a staggered round robin approach to control distribution of power within the computer cart without requiring the amount of power used from each power strip to be individually monitored.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/472,797, filed May 16, 2012, which claims priority to U.S.Provisional Patent Application No. 61/595,427, filed Feb. 6, 2012, thecontent of each of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to storage systems and, more particularly,to a cart designed to house and store portable computing devices.

2. Description of the Related Art

Portable computing devices, such as laptop and tablet computers, arecommonly used in educational facilities to enrich the curriculumprovided to students. Likewise, these types of devices are increasinglybeing used in other contexts, such as in museums, to enable people tointeract with the exhibits present in the museum.

Portable computing devices typically include a battery that may becharged to enable the portable computing devices to be used while notconnected to an electrical outlet. Since most batteries are chargedusing relatively low voltage DC power (e.g. 19.5 volt or 24 volt), atransformer is commonly used to convert 120/240 volt 60/50 Hz ACelectrical power available in a standard electrical outlet to the lowervoltage DC power required by the device. Transformers of this type usedto convert line power for use by laptop computers have commonly becomeknown as “bricks”. Generally, bricks are computer specific, in that eachtype/model of computer may have its own transformer depending on theparticular power characteristics of that specific computer.

Computer carts have been developed which may be used to store portablecomputing devices in a secure manner. Often, the portable computingdevices will be electrically connected within the cart to enable theportable computing devices to be charged and synchronized while storedin the cart. Because the computer bricks are required to interconnectthe computers to an electrical power source, the cart must also bedesigned to accommodate the computer bricks. Where the cart is designedto hold multiple portable computing devices such as 24-36 computers,installation of the computer bricks and associated power cords, as wellas storage of the bricks and power cords within the computer cart, maypresent challenges. Likewise, when changing between computer types orupgrading computers, it may be necessary to remove all the wiring andassociated bricks from the cart and reinstall the new bricks andassociated power cords, which can take a considerable amount of time.Accordingly, it would be advantageous to provide a new type of computercart with improved transformer and power cord storage, installation, andmaintenance capabilities.

SUMMARY OF THE INVENTION

The following Summary and the Abstract set forth at the end of thisapplication are provided herein to introduce some concepts discussed inthe Detailed Description below. The Summary and Abstract sections arenot comprehensive and are not intended to delineate the scope ofprotectable subject matter which is set forth by the claims presentedbelow.

A computer cart has removable electrical connector management systemwhich may be removed from the computer cart to install portableelectronic device electrical transformers, and then reinserted into thecomputer cart to enable multiple electrical transformers to be installedinto the cart as a group. An electrical charging system uses a staggeredround robin approach to control distribution of power within thecomputer cart without requiring the amount of power used from each powerstrip to be individually monitored.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are illustrated by way of example inthe following drawings in which like references indicate similarelements. The following drawings disclose various embodiments of thepresent invention for purposes of illustration only and are not intendedto limit the scope of the invention. For purposes of clarity, not everycomponent may be labeled in every figure. In the figures:

FIG. 1 is a front perspective view of a computer cart according to anembodiment;

FIG. 2 is a front perspective view of the computer cart of FIG. 1 withthe doors opened to show a computer storage compartment of the computercart;

FIG. 3 is a rear perspective view of the computer cart of FIG. 1 withthe doors removed to show a cord management compartment of the computercart;

FIG. 4 is an expanded view of the structure shown in FIG. 3 showing aremovable electrical transformer attachment panel;

FIG. 5 is an perspective view of the removable electrical transformerattachment panel of FIG. 4;

FIGS. 6-7 show sequential steps of inserting the removable electricaltransformer attachment panel into the cart of FIG. 1;

FIG. 8 shows an expanded view of an attachment detail showing theremovable electrical transformer attachment panel attached to a backpanel of the computer cart; and

FIG. 9 is a functional block diagram of an electrical power distributionsystem according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of one embodiment of a computer cart 10designed to maintain a large number of portable computing devices suchas laptop computers and tablet computers. In the view of FIG. 1, thedoors of the computer cart are closed to show how the cart appears whenclosed for storage. The exterior of the cart may be of arbitrary designand the invention is not limited to a cart having the particularaesthetic appearance of the cart shown in FIG. 1.

In general, the computer cart shown in FIG. 1 has an exterior sheathingwhich may be vented as appropriate to enable heat generated by chargingcomputers to be released from the cart. Depending on the particularconfiguration of the ventilation system, the ventilation system may bepassive or active. The exterior of the cart generally protects thecomputers from being accessed while being stored within the cart. Thecart also has wheels 12 to enable the cart to be mobile. The wheels maybe implemented as castors which may be directionally locking and/ormotion locking depending on the particular embodiment. Doors 14 on thefront of the cart allow access to an interior computer storage areawhere the portable computing devices are stored in the cart. The doorsmay be locked to prevent unauthorized access to the computers storedtherein. The front compartment where computers are stored will bereferred to herein as the computer storage area. A compartment in therear of the computer cart, which also is accessible via a similar set ofdoors, will be referred to herein as a cord management storage area.

FIG. 2 shows the cart of FIG. 1 with the doors 14 opened to reveal theinterior of the cart. In the embodiment shown in FIG. 2, the computercart 10 generally is formed as a cabinet having an interior framingstructure 16 which is used to support one or more shelves 18. Theexterior sheathing of the computer cart is also attached to the interiorframing structure 16. A floor 20 forms a bottom of the computer cart 10.Dividers 22 are provided to separate the computer storage area intoindividual computer storage compartments sized to hold the computers. Inthe embodiment shown in FIG. 2, the computer cart is sized to hold 30computers. Other numbers of compartments may be included as well.

Each individual computer storage compartment is defined by a pair ofdividers which physically separate the compartment from an adjacentstorage compartment so that the computers are able to be held verticallywithin the cart. Each computer storage compartment is designed to hold asingle portable computer. In the embodiment shown in FIG. 2, theindividual computer storage compartments are included within the cart onmultiple shelves which enable two rows of portable computing devices tobe stored within the computer cart. In other embodiments thecompartments may be arranged in different ways to enable other numbersof computers to be stored within the cart.

FIG. 3 shows a rear cord management storage area 20 designed to storetransformers and associated power cords for the computers stored in thecomputer cart. In the view shown in FIG. 3 the doors have been removedto allow the interior of the cord management storage area to be visible.Doors similar to the doors 14 shown in FIG. 1 may be included to allowaccess to the cord management storage area to be restricted, so that thetransformers are not unintentionally or intentionally unplugged and/orremoved from the cart. In another embodiment, a fixed back panel may bescrewed onto the computer cart to restrict access to the interior of thecord management storage area.

As shown in FIG. 3, the cord management compartment includes powerstrips 22, each of which includes six individual power outlets 24. Eachpower strip corresponds to a charging zone as described in greaterdetail below. Although the power strips are shown as having 6 outlets,since each power strip in the illustrated embodiment is designed toprovide power to a zone of five computer storage compartments, inanother embodiment a different number of outlets may be incorporated ineach power strip 22.

A removable electrical transformer attachment panel 26 is provided foreach zone to hold electrical transformers for computers stored inassociated compartments of the cart. Apertures 28 allow power cords tobe passed from the rear cord management area to a respective computerstorage compartment in the computer storage area. To facilitatecorresponding a transformer with a computer stored in a particularcomputer storage compartment, the apertures 28 are numbered. Theindividual computer storage compartments are likewise numbered withcorresponding numbers so that a computer storage compartment may beuniquely identified with a corresponding brick storage location in therear cord management area.

To enable electrical transformers to be installed in the cart, in oneembodiment, the electrical transformer attachment panels are removable,as shown in FIG. 4. In operation, when transformers are to be insertedinto the cart, the electrical transformer attachment panel may beremoved as shown in FIG. 4. Electrical transformers may then be attachedto the transformer attachment panel, such as by using plastic cableties, and the transformer attachment panel and associated transformersand power cords may be re-inserted into the cart as a unit. Other waysof attaching the transformers to the transformer attachment panel may beused as well, such as zip ties, wire ties, Velcro straps, nylon orplastic ties, wire ties such as twist ties or stainless steel ties, andelastic straps. Slots 29 are provided to enable the ties to pass throughthe electrical transformer attachment panel. In one embodiment, as shownin FIG. 4, pairs of slots 29 define electrical transformer attachmentareas 30 designed to individually hold electrical transformers.

A shelf 32 is provided on a lower edge of the electrical transformerattachment panel 26. The shelf 32 prevents the electrical transformersfrom extending beyond a lower edge of the electrical transformerattachment panel so that, when the electrical transformer attachmentpanel is reinserted into the cart, the electrical transformers do notimpinge on the power strips 22. This facilitates insertion of theelectrical transformer attachment panels back into the rear cordmanagement area by ensuring proper positioning of the transformers onthe electrical transformer attachment panel.

FIG. 5 shows an electrical transformer attachment panel in greaterdetail. As shown in FIG. 5, the electrical transformer attachment panelincludes a pair of side walls 34 designed to allow the electricaltransformer attachment panel to stand a particular distance off a backwall of the rear storage compartment. This provides for air circulationas well as allows for clearance between the back wall of the cart andthe rear surface of the electrical transformer attachment panel toaccommodate rear tabs 36 of dividers 22. The rear tabs 36 are used toallow the dividers to be held in a vertical position by the rear wall toprovide additional stability to the dividers. If the dividers were to bedesigned differently, the clearance between the rear surface of theelectrical transformer attachment panel and the back wall of the rearstorage compartment may be adjusted accordingly.

Depending hooks 38, 42, on the side walls of the electrical transformerattachment panel are designed to engage slots 40, 44, in the back wallof the rear storage compartment. In one embodiment, the upper dependinghook 38 is sized to have a downwardly extending prong 46 separated froma back edge of the side wall 34 by a gap 48. The width of this gap, inone embodiment, is approximately the width of a thickness of the backwall of the rear storage compartment. Likewise the lower depending hook42 is designed to have an extending prong that is similarly positionedapproximately a thickness of the back wall of the rear storagecompartment away from the back edge of the side wall, and extend belowthe shelf 32.

In operation, depending hooks 38, 42 are inserted into slots 40, 44, andthe removable electrical transformer attachment panel 26 is sliddownward so that downwardly extending prongs 46 slide behind the backwall of the rear storage compartment. This holds the electricaltransformer attachment panel in place relative to the back wall. Toremove the electrical transformer attachment panel, the electricaltransformer attachment panel is slid up relative to the back wall untilthe depending hooks no longer engage the back wall. Optionally a setscrew or other mechanical fastener (not shown) may be used to secure theelectrical transformer attachment panel in place while engaged with theback wall.

FIGS. 6-8 show how the electrical transformer attachment panel issecured to the back wall. As shown in FIG. 6, the electrical transformerattachment panel is lined up with the back wall such that dependinghooks 38, 42 are aligned with slots 40, 44. The depending hooks are theninserted into the respective slots and the electrical transformerattachment panel is slid down relative to the back wall so that thedownwardly extending prongs 46 engage the back surface of the back wall.

Gravity will hold the electrical transformer attachment panel in thisposition. Optionally, as shown in greater detail in FIG. 8, a frictionalfit between the back edge of the side wall 50, the back wall 52, and aninner edge 54 of the downwardly extending prongs 46 may also help holdthe electrical transformer attachment panel in place relative to theback wall. A mechanical fastener such as a set screw (not shown) mayalso be used to hold the electrical transformer attachment panel inplace.

FIG. 9 shows an embodiment of an electrical system for use in a computercart such as the cart shown in FIGS. 1-8. As shown in FIG. 9, in oneembodiment line power is received on line 100. Optionally an on/offswitch may be used to selectively connect the cart to line power,although this option has not been shown in FIG. 9. The voltage on line100 is sensed by voltage sensor 102 and an indication of the sensedvoltage value is transmitted to microcontroller 104. Sensing the voltagevalue allows the cart to automatically adjust operation characteristicsfor 110/220 volt line power. For example, if the voltage sensor detectsa line voltage above a threshold, such as above 164 volts, themicrocontroller may cause the cart charging system to adjust to assumean input voltage of 220 volts, which is a standard line voltage inEurope and numerous other countries. A detected line voltage below thisthreshold, by contrast, will cause the microcontroller to assume aninput voltage of 110 volts, which is the standard line voltage in NorthAmerica.

The current being drawn by the cart is also sensed by current sensor106. In one embodiment, the power distribution system is powered from a15 or 20 amp rated 90-130 VAC circuit or a 10 amp rated 208-264 VACcircuit. The maximum steady state current draw may be limited to 80% ofthe rated current: 12 amps for a 15 amp circuit, 16 amps for a 20 ampcircuit, or 8 amps for a 10 amp circuit. As noted above, the linevoltage threshold is used to control operation of the power system. Ifthe current is above the threshold, the microcontroller will assume 220volt operation and assume the lowest current setting. If the current isbelow the threshold, the current will be limited at 12 or 15 ampsdepending on the capacity of the input circuit.

The power management system controls distribution of power within thecart to each zone by switching the zones independently on or off basedon the total current draw, as measured by current sensor (amp meter)106. Specifically, microcontroller 104 controls operation of switches108A-108H, which individually control distribution of power to powerstrips 110A-110H. In operation, microcontroller individually controlsoperation of switches 108A-H to individually control application ofpower to power strips 110A-H to selectively charge computers pluggedinto the outlets of the power strips. Referring back to FIG. 3, in oneembodiment, each power strip 22 of the embodiment shown in FIG. 3 maycorrespond to one of the power strips 110A-110H.

To provide power to computers within the cart in an equitable manner,the microcontroller controls distribution of power to the computers inthe charging zones in a staggered manner over time, such that eachcharging zone receives power for at least a portion of the totalcharging period, while preventing the cart from drawing too much powerto overload the circuit associated with line power 100. In theillustrated example there are 8 switches controlling 8 charging zones.Other numbers of switches and charging zones may be controlled as well.The charging zones may be implemented as one or more power strips 22, asshown in FIG. 3, or using other electrical outlets.

The microcontroller controls switch 112 that controls application ofpower to auxiliary output 114. In one embodiment, power is alwaysapplied to the auxiliary output 114 as long as it does not exceed thespecified current limit. The auxiliary power output may be used, forexample, to allow a computer, television, printer, or other device toobtain power from the computer cart.

Likewise, microcontroller 104 controls switch 116, which controlsapplication of power to network switch 118. The network switch, in oneembodiment, is powered off until the total current draw of all outputsis below a specified limit. Network switch 118 may be, for example, awireless network switch to enable the cart to act as a WiFi (IEEE802.11) hotspot or, alternatively, may be an Ethernet switch to enablethe cart to be connected to a wired network. This allows the computersto be connected to a computer network while stored within the computercart. Other types of network switches may be used as well to enable thecomputers contained within the cart to connect with each other and withan external network.

In one embodiment, if the total current draw of all 10 outputs(auxiliary 114, network switch 118, and power strips 110A-H), exceedsthe total available current on line 100, the microcontroller will causethe power strips to be turned on in groups of 1 or more for shortperiods of time, referred to herein as cycles. For example, a chargingcycle may be three minutes long. The particular length of the cycle mayvary according to the particular implementation. The groupings, in oneembodiment, are optimized to power the most outputs possible withoutexceeding the current limit.

In one embodiment, the microcontroller will cause power to be applied toa first power strip such as power strip 110A, and sense the amount ofcurrent drawn by the computers connected to the power strip 110A. If theamount of current drawn by power strip 110A does not exceed the currentlimit for the given mode of operation, the microcontroller 104 will thencause power to also be applied to a second power strip in apredetermined rotation, such as power strip 110B. This process continuesuntil the current limit is reached. The group of power switches selectedin this manner will be charged during the cycle, e.g. for three minutes,and then a new group of outputs will be selected.

When selecting a new group of outputs, the microcontroller willinitially select another of the power strips, such as power strip 110B,and cause power to be applied to that power strip. The microcontrollerwill sense the amount of current drawn by that power strip and, if thetotal amount of power drawn by the cart does not exceed the currentlimit for the mode of operation, will activate the next successive powerstrip 110C. In this manner, the microcontroller uses a staggered roundrobin approach to select a group of output power strips arranged in apredetermined rotation order to receive power during successive chargingcycles.

Table I shows an example selection of charging zones (power strips)during successive cycles. In Table I, the first column (labeled “1zone/cycle”) assumes that the power consumption on a given power stripis sufficiently great to consume all available power in the cart. Hence,during each successive cycle only one of the power strips will receivepower. The second column (labeled “2 zones/cycle”) shows the selectionof power strips in a scenario where two power strips are able to bepowered during each cycle. The third and fourth columns (respectivelylabeled “3 zones/cycle” and “4 zones/cycle”) similarly show theselection of power strips where respectively three and four power stripsare able to be powered during each cycle:

TABLE I 1 zone/cycle 2 zones/cycle 3 zones/cycle 4 zones/cycle cycle 1110A 110A + 110B 110A + 110B + 110C 110A + 110B + 110C + 110D cycle 2110B 110B + 110C 110B + 110C + 110D 110B + 110C + 110D + 110E cycle 3110C 110C + 110D 110C + 110D + 110E 110C + 110D + 110E + 110F cycle 4110D 110D + 110E 110D + 110E + 110F 110D + 110E + 110F + 110G cycle 5110E 110E + 110F 110E + 110F + 110G 110E + 110F + 110G + 110H cycle 6110F 110F + 110G 110F + 110G + 110H 110F + 110G + 110H + 110A cycle 7110G 110G + 110H 110G + 110H + 110A 110G + 110H + 110A + 110B cycle 8110H 110H + 110A 110H + 110A + 110B 110H + 110A + 110B + 110C cycle 9110A 110A + 110B 110A + 110B + 110C 110A + 110B + 110C + 110DAs shown in Table I, if the computers connected to the power strips aredrawing a large amount of current, and the microcontroller is only ableto charge one power strip at a time, it will cycle through each of theavailable power strips. As the computers become charged, they will drawless current, thus allowing larger numbers of power strips to be turnedon without exceeding the current limit for the computer cart. Thus, forexample, when three strips are able to be charged, during cycle 1 thecart will provide power to power strips 110A-C, in cycle 2 the cart willprovide power to power strips 110B-D, etc. By starting with a nextsubsequent strip at each cycle the microcontroller is able to guaranteepower to every power strip, while providing power to as many powerstrips as possible during each charging cycle.

Table I shows application of the staggered round robin approach whereall power strips are drawing relatively similar amounts of power.Realistically, it may be expected that there would be instances wheresome of the power strips will not draw any power, some power strips maydraw a considerable amount of power, and other power strips may drawonly a little bit of power. These differences in power demand may stemfrom different numbers of computers being plugged into the differentpower strips and may also depend on how charged/discharged the computerbatteries are. Table II shows an example of application of the staggeredround robin approach to distribution of power over a series of cyclesassuming the cart is operating at a 12 amp current limit, while assumingthe power strips are requiring the following levels of power:

power strip 110A 4 Amps power strip 110B 1 Amps power strip 110C 3 Ampspower strip 110D 7 Amps power strip 110E 3 Amps power strip 110F 0 Ampspower strip 110G 1 Amps power strip 110H 1 Amps

TABLE II combination of power strips active total current draw cycle 1110A + 110B + 110C 4 + 1 + 3 = 8 cycle 2 110B + 110C + 110D 1 + 3 + 7 =11 cycle 3 110C + 110D 3 + 7 = 10 cycle 4 110D + 110E 7 + 3 = 10 cycle 5110E + 110F + 110G + 110H + 3 + 0 + 1 + 1 + 4 + 1 = 10 110A + 110B cycle6 110F + 110G + 110H + 110A + 0 + 1 + 1 + 4 + 1 + 3 = 10 110B + 110Ccycle 7 110G + 110H + 110A + 110B + 1 + 1 + 4 + 1 + 3 = 10 110C cycle 8110H + 110A + 110B + 110C 1 + 4 + 1 + 3 = 9 cycle 9 110A + 110B + 110C4 + 1 + 3 = 8

As shown in FIG. 2, in operation the number of powered strips will varydepending on the current draw associated with the particular selectedstrips. The microcontroller will activate one strip, determine theamount of power drawn during steady state by that strip (e.g. after 5seconds) and if there is sufficient power continue selecting additionalstrips to receive power until the computer cart current limit has beenreached. This will iterate giving each power strip preference (initialselection) until all power strips have been prioritized, at which pointthe microcontroller will repeat once again selecting the initial powerstrip as the priority power strip. As all computers within the cartbecome closer to fully charged, it may be expected that power may beapplied to all of the power strips. Specifically, as the computers arecharged, the current drawn by the computers will decrease thus allowingthe microcontroller to select larger numbers of strips during eachcharging cycle.

By using a single current meter for the computer cart, the overallcurrent consumed by the cart may be maintained at a level to ensure thatthe current drawn will not exceed the available line current. Further,by incorporating feedback from this current sensor during the zoneselection process, the microcontroller can provide power to an adaptivenumber of power strips without individually monitoring the amount ofcurrent being drawn by any particular power strip. This simplifies theelectronic system while continuing to optimize performance of the powersystem to provide power to optimal groupings of power strips based onthe amount of power being drawn by the power strips.

The functions described herein may be implemented as programmable logicused in conjunction with a programmable logic device such as a FieldProgrammable Gate Array (FPGA) or microprocessor such as microprocessor104. Alternatively, these functions may be implemented a set of programinstructions that are stored in a computer readable memory and executedon one or more processors. Programmable logic can be fixed temporarilyor permanently in a tangible medium such as a read-only memory chip, acomputer memory, a disk, or other storage medium. All such embodimentsare intended to fall within the scope of the present invention.

It should be understood that various changes and modifications of theembodiments shown in the drawings and described in the specification maybe made within the spirit and scope of the present invention.Accordingly, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings be interpreted in anillustrative and not in a limiting sense. The invention is limited onlyas defined in the following claims and the equivalents thereto.

What is claimed is: 1-17. (canceled)
 18. A computer cart, comprising: acomputer storage compartment; and a power distribution system,comprising: a current sensor connected to a power input line; amicroprocessor operably connected to the current sensor for receiving anindication of a sensed current on the power input line, themicroprocessor containing programmable logic to cause the microprocessorto activate charging zones on a staggered round robin basis.
 19. Thecomputer cart of claim 17, wherein each charging zone comprises a set ofoutlets.
 20. The computer cart of claim 17, wherein each charging zonecomprises a power strip having a set of outlets.
 21. The computer cartof claim 17, wherein the charging zones are arranged in a predeterminedorder.
 22. The computer cart of claim 17, wherein the charging zones donot include individual current sensors.
 23. The computer cart of claim17, wherein the microprocessor activates charging zones on a staggeredround robin basis by: selecting a first charging zone; determining anamount of current drawn by the cart from the current sensor; and whenthe current drawn by the cart does not exceed a threshold, selecting asecond charging zone from the available charging zones, and sequentiallyselecting additional charging zones according to a predetermined orderuntil the current drawn by the cart approaches the threshold.
 24. Thecomputer cart of claim 23, wherein the microprocessor activates chargingzones on a staggered round robin basis by: charging the selected groupof charging zones for a first period of time; and selecting a new groupof charging zones for a second period of time.
 25. The computer cart ofclaim 24, wherein the new group of charging zones is selected by firstselecting the second charging zone.
 26. A computer storage system,comprising: a computer storage compartment; and a power distributionsystem, comprising: a current sensor connected to a power input line; amicroprocessor operably connected to the current sensor for receiving anindication of a sensed current on the power input line, themicroprocessor containing programmable logic to cause the microprocessorto activate charging zones on a staggered round robin basis.
 27. Thecomputer storage system of claim 26, wherein each charging zonecomprises a set of outlets.
 28. The computer storage system of claim 26,wherein each charging zone comprises a power strip having a set ofoutlets.
 29. The computer storage system of claim 26, wherein thecharging zones are arranged in a predetermined order.
 30. The computerstorage system of claim 26, wherein the charging zones do not includeindividual current sensors.
 31. The computer storage system of claim 26,wherein the microprocessor activates charging zones on a staggered roundrobin basis by: selecting a first charging zone; determining an amountof current drawn by the cart from the current sensor; and when thecurrent drawn by the cart does not exceed a threshold, selecting asecond charging zone from the available charging zones, and sequentiallyselecting additional charging zones according to a predetermined orderuntil the current drawn by the cart approaches the threshold.
 32. Thecomputer storage system of claim 31, wherein the microprocessoractivates charging zones on a staggered round robin basis by: chargingthe selected group of charging zones for a first period of time; andselecting a new group of charging zones for a second period of time. 33.The computer storage system of claim 32, wherein the new group ofcharging zones is selected by first selecting the second charging zone.